Dehydration of caustic alkali.



UNITED FFKCE;

rant ERWIN-OBERREIT, or LUDWIGSfiAF-EN-ON THE-RHINE,, AND rmnnmcn MORITZ JAHRMARKT, or MANNHEIM, GERMANY, ASSIGNORS T BADISC'HE 'ANILIN & SODA FABRIK, OF LUDWIGSHAFEN-OIlSl-THE-RHINE, GERMANY.-

DEHYDRA'VIION or CAUSTIC ALKAIJ.

No Drawing.

' To all whom it concern. I

I Thisliquor was removed from the vacuum- Be it known that we,'PAULERwIN 'OBER- REY/1 and F RIEIiRIoH Mom'rz JA-HRMARKT, doctors of, philosophy and chemists, subjects of the King of Saxony, residing, respecti'vely, at Ludwigshafen-omthe-Rhine, in the Kingdom of Bavaria, and Mannheim,

in the Grand Duchy of Baden, German Em pire, have invented new and useful provements in the Dehydration of Caustic Alkali, ofwhich the following is ,a specifi cation. j I

When manufacturing caustic alkalis by treatingthe carbonates with caustic lime, the caustic alkali is first obtained in the form of a dilute solution. The old method of obtaining solid caustic alkali from this consisted first of all in concentrating the crude soda lye .in a vacuum evaporator continuing the evaporation until the impurities in the lye began to separate out, that isto say, until the solution contained about 22% of caustic soda and more than 75% of water.

' Letters Patent No. 12,320, the process which consists in heating thealkali which contains water in an open Vessel while passing an electric current through the alkali, using the vessel as one of the electrodes, was described.

This also, however, has disadvantages, since.

a considerable quantity of alkali superoxid is formed and this renders the caustic alkali useless for some purposes, such tor instance as in. the preparatlon of indigo.

We have now discovered that the water can be removed from caustic alkaliswhich,

are solid at ordinary atmospheric temperatures and the said alkalis be obtained in'a 50.

dehydrated condition by heating the said alkalis in vacuo. For instance, by heating caustic soda in 'oacuo ata temperature of about one hundred and eighty degrees cen- Specification of Letters Patent. Application filed September 8, Serial No. 277,499.

Various methods of avoiding the.

PatentedFeb. 7, 1911.

i tigrade, or by heating caustic potash in cacao at a temperature of about two hun dred andslxty'degrees centigra-de, that is, at

temperaturesbelow those at which the caustic soda and caustic potash, respectively, I

condition, while the vessels (which may be tically unattacked and therefore last much longer,.and dehydrated alkalis are obtained which contain only tracesxof'foreign metals. Of course, temperatures higher than those aforesaid can be employed so long as the vessel remains unattacked, and temperatures lower than those aforesaid can be employed, but in the latter case, the dehydration proceeds more slowly and scarcely to the same extent. Since cautic alkali, containing, say, 10% of water attacks iron at temperatures above about 400 0., ,We carry out the dehydration according to our invention at tem- ,peratures between 170 C. and 400 C.

It is known that dilute caustic alkaline solutlons can be concentrated in oacuo, andthis method of concentration has been prac- -melt, they can be obtained 'ina dehydrated not iron)'fin which they-are heated are practiced to obtain caustic alkali solutions -c'ontaining up to about fifty per cent. of caustic alkali, and it has been proposed to concentrate heavy lyes by distributing the lye in a' thin layer upon the heated inner surface ofa vacuum vessel provided with a special ap-' paratus and thus obtaining a product containing as little as fifteenper centJof water, and no claim is made to these processes, but it. hasnot hitherto been known that any advantageous effect 'could beobtained by heating in an ordinary vacuum apparatus caustic potash, or caustic soda, which are so fanfree from water that they are solid at ordinary atmospheric temperatures, and it is our discovery that such solidcaustic potash and solid caustic soda will entirely part with their water in vacuo at such low temperature that it is possible to effect the complete dehydration without the vessels employed being attacked to any objectionable extent and with practically no contamination of'the resulting product. When starting with either such solid caustic soda, or such solid caust-iepotash, containing but little water, it can, if desired, be completely dehydrated according to our invention, without the caustic alkali melting.

Instead of treating caustic potash, or caustic soda, alone, of course a mixture of the two may be treated according to our invention. a a

Although by the process according to our invention complete dehydration can be effected and it is the object of our invention to effect this, yet in the expressions dehydrated and dehydration we include such degree of dehydration beyond that hitherto obtained as will give, for practical purposes, the benefit ofour invention, and we do not claim the production of caustic alkali coni taining more than ten (10 per cent. of water. The following examples will serve to illus-,

trate how ourinvention can be carried into I gI'eeseentigI-ade), at a slightly higher te iiriperafure 'dissolve in the water contained in it. Such acaustic soda is for instance one containing sixty per cent. of NaOH and meltiiig at %0. The mass, which is at first -liquid, afterward becomes thick and finally becomes solid, and when suitable stirring apparatus is employed, it can he obtaine as a powder. a r Example 2: Heat,.z'noao'uo, at atemperature of two hundred'andsixty (26 degrees centigrade, while stirring, one hundred (100) parts of caustic potash-,which is olid at Q I ordinary atmospheric temperatures say fiftween '(15) degrees centigrade -but whigh,

on slightly heating, dissolves in the water contained in it. "Such a caustic potash is for instance one containing-fi'ityeight per cent. of KOH and meltingat 32 C. Continue the heating so long as any water distils ofi. The reaction proceeds as de's'c'ribedi in- Example 1.

-l fE'in this example, a temperature'of from one hundred and eighty (180;) to 'two hundred (200) degrees centigrade be maintained till about thirty-seven "parts of water have distilled ofl, a technically pure caustic pot- 'centigrade, while stirrin scribing Witnesses. 7

ash, of about ninety r e t, ig b i tained. I Example 3: Heat, in vacuo, ,at a temperature of two hundred and sixty (260) degrees g molecular proportions of a mixture of equn v caustic soda andf caustic" potash each solid at ordinary atinos-i phe'ric temperatures (say fifteen degreesi -i'l centigrade), but containing so much wateras to yield a solution upon slightly heating;

Such a mixture is for instance one containing sixty-three per cent. of the mixed alkalis.

and thirty-seven parts of water and melting at about C. In this case the mass, at the temperature of the melt, remains liquid after complete dehydration has taken place.

Example 4:: Grind, to a fine powder, commercial caustic pot-ash containing for in stance seventy per .cent. of pure caustic potash and melting at about 140-145QC. and then heat it, in vacuo, gradually raising the temperature toabout two hundred and sixty (260) degrees centigrade andmaintain this temperature until no more water distils off.

Now what we. claim is:

1 The process of obtaining caustic alkali from solutions thereof which/consists in con centrating the caustic alkali solution until it has reached the point at which it would act upon the .material of the containing vessel,

.and then further concentrating in vacuo at a temperature sufiiciently low to preventaction of the material of the vacuum drier but sufiiciently high to drive off substantially all of the water.

2. The process of obtaining caustic alkali from solutions thereof which consists in concentrating the caustic alkali solution until it has reached the point at which it would act upon the material of the containing vessel and then further concentrating in. 'vacuo at a temperature of about 180 to 260 C.

In testimony whereof we have hereunto set our hands in the presence of two sub rim. .ERWIN OBERREI'L.

'- FRIEDRICH MORITZ JAHRMARKT.

Witnesses:-

J. Arno. LLOYD, Jos. H. LEU'I'E. 

